The present invention relates to a material suitable for heat sensitive recording papers, and more particularly to a heat sensitive recording material characterized by containing a specific developer capable of bringing a color forming substance into color images by heating.
The heat sensitive recording paper is a recording material in which a heat sensitive layer which can be developed a color by heating is applied to a surface of a substrate such a paper. The recording process is conducted by using a printer such as a thermal printer. The paper is widely utilized in the field of computers, facsimile telegraphs, calculating machines, and the like.
The heat sensitive layer is composed of a composition containing a color forming substance, a developer capable of bringing the color forming substance into color images and a binder, and it is said that the developer is the most influential component to properties of the heat sensitive recording material among the above three components. Accordingly the utility of the heat sensitive recording materials depends on the properties of the used developer.
Bisphenol A has been most numerously used as the developer which brings a colorless dye of electron donor such as Crystal Violet lactone into color images. However, recently, the bisphenol A developers have not been coping with the high speed of printing process, and bis(hydroxyphenyl)acetic acid developers are paid attention instead of the above bisphenol A developers as shown in Japanese Unexamined Patent Publication No. 5288/1983 or Japanese Unexamined Patent Publication No. 79793/1984, and the like.
The heat sensitive recording material containing the bis(hydroxyphenyl)acetic acid developers are excellent in not only the smoothness of recording paper but also the printability at recording process of high speed compared to the material using bisphenol A developers, and accordingly, the desirable results can be obtained from the point of the resolution. However, the thermal printers are improved day after day in order to attain more excellent functions such as heat energy is further economized. Accordingly, it is required to further improve the properties of the heat sensitive recording material, particularly the developer in order to fit the improved functions of the printers. That is, it is required to obtain the developer which can give satisfactory color sensitibity, color density and the excellent resolution at recording process of lower temperature for a short time.
Also, in the known heat sensitive recording materials, a part of the color forming substance is apt to color-develop before printing and accordingly there is observed the black fog on the surface of recording papers which should be white originally, or the recording papers are remarkably blackened by contacting with the diazo photosensitive papers to disappear the printed images.
It is an object of the present invention to provide a heat sensitive recording material free from the above-mentioned defects.
This and other objects of the present invention will become apparent from the description hereafter.